Gas dosimeter using colorimetric strip also sensitive to light



Dec. 9,` 1969 C. A. PLANTZ GAS DOSIMETER USING COLORIMETRIC STRIP ALSO'SENSITIVE TO LIGHT Filed May 2. 196'? United States Patent O 3,482,944GAS DOSIMETER USING COLORlMETRIC STRIP ALSO SENSITIVE T LIGHT Charles A.Plantz and Cecelia C. Jenca, Pittsburgh, and Paul W. McConnaughey,Wilkinsburg, Pa., assignors to Mine Safety Appliances Company,Pittsburgh, Pa., a corporation of Pennsylvania Filed May 2, 1967, Ser.No. 635,499 Int. Cl. G01n `i1/08; G01j 3/48 U.S. Cl. 23-254 7 ClaimsABSTRACT 0F THE DISCLOSURE It is among the objects of this invention toprovide a dosimeter which can detect a given gas by the use ofcolorimetric material that is sensitive to light, and which is simple inconstruction and extremely easy to use.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which:

FIG. 1 is a front view of our dosimeter;

FIG. 2 is a view similar to FIG. 1, but showing the dosimeter open;

FIG. 3 is a central vertical section taken on the line III- III of FIG.1; and

FIG. 4 is a horizontal cross section taken on the line IV-IV of FIG. l.

Referring to the drawings, a rectangular open front receptacle 1 isformed from any suitable material such as a molded plastic. Thereceptacle has a back wall and forwardly projecting side walls aroundits four sides. The receptacle is intended to be worn on a personsclothing, such as by suspending it from a spring clip 2 by means of astrap 3 that may be looped through a slot 4 in the top side wall of thereceptacle.

As shown in FIG. 3, the central portion of the back Wall is outsetrearwardly or outwardly to form a long narrow recess 6, the lower end ofwhich is provided with a transverse slit 7. Sealed into the front ofthis recess is a partition 8 provided near its upper end with an opening9. Most of the partition is opaque, but preferably a short length of itdirectly below the opening is transparent and colorless to form a clearwindow 10. A convenient way of making the partition is to make it ofglass or clear plastic that is covered with an opaque paint except forthe window area and opening 9. The recess between the offset portion ofthe back of the receptacle and the partition forms a thin pocketintended for receiving a strip 12 of colorimetric material which can beinserted through the slit 7 at the bottom of the pocket. To hold thestrip in the pocket and also for another purpose to be described later,springs are mounted in the pocket behind the strip and press it forwardagainst the partition. A convenient form for the springs to take is apair of parallel spring wires 13 having bent ends anchored in holes inthe rear wall of the pocket, with the intermediate portions of thesprings bowed forward to press against the strip.

When a gas-sensitive colorimetric strip is exposed to the gas to bedetected, the color of the strip changes and the degree of color changeindicates the product of the concentration of the gas in the atmospheremultiplied by the exposure time, as is well known. This change in color3,482,944 Patented Dec. 9, 1969 ICC can be viewed through the opening 9in the front of the pocket. The color of the strip then is compared withcolor standards 14 located near the exposed portion of the strip. Thesecolor standards are colored plaques, insensitive to light, that may beglued to the back wall of the receptacle around opening 9. Colors areselected that will indicate certain concentrations of the gas inquestion.

The colorimetric strips intended for use with this dosimeter are a typethat not only are sensitive to a gas, but also are sensitive to actiniclight. Such strips are used for detecting hydrazine, substitutehydrazines, and certain other volatile gases in air. For detectinghydrazine, for example, the colorimetric material may be formed byimpregnation of bindone in some porous substance, such as paper or thinlayer chromatography material or the like. If this colorimetric materialis exposed to direct light for very long, the light will cause achemical reaction that will reduce the sensitivity of the strip andtherefore the strip will give a false reading of the gas being detected.It is therefore a feature of this invention that the colorimetric stripin the back of the receptacle is protected from direct light. This isaccomplished by means of a shield 16 mounted in the receptacle in frontof pocket 6. The shield is spaced from the back wall of the receptacleand from some or all of its side walls so as not to prevent thecolorimetric strip from being exposed to the atmosphere surrounding thedosimeter. The shield and receptacle preferably are black or some othercolor that absorbs actinic light in order to reduce reflection of thatlight onto the sensitive strip.

The shield can be removed temporarily so that the portion of the stripviewed through opening 9 can be cornpared in color with the surroundingcolor standards. A preferred way of mounting the shield in thereceptacle and providing for its removal from in front of the strip isto hinge the lower end of the shield to the receptacle. This can be doneby providing the lower ends of the opposite sides of the shield withrearward projecting parallel lugs 17, through which a hinge pin 18extends, as shown in FIGS. 3 and 4. The ends of the pin are sprung intoholes in the vertical side walls of the receptacle. A torsion spring 19is mounted on the pin, with one end of the spring hooked under the lowerend of the shield and the outer end pressing against the back of thereceptacle. This spring normally holds the shield in a vertical positionentirely within the receptacle. This is the closed position of theshield. The upper end of the shield is provided with a short leg 20 tospace it from the back of the receptacle. In order to open the shield,its lower portion is provided with an outwardly projecting tab 21 thatcan be pressed down by the thumb or a finger to cause the upper end ofthe shield to swing forward out of the receptacle and down to asubstantially horizontal portion, as shown in FIG. 2. This will exposeopening 9 fully to view for checking the color of the strip with thecolor standards.

Although short exposures of the colorimetric strip to light will notaffect its sensitivity, it is preferred that the dosimeter beconstructed in such a way that it is not necessary to swing the shieldout of the receptacle in order to see whether the colorimetric strip haschanged color. Consequently, the shield is provided with a centralopening 23, through which the strip can be seen. However, to preventactinic light from reaching the strip through this opening and affectingits color by reducing its sensitivity, a light lter 24 is mounted in theopening to form a window. This lter is a plastic or glass of a colorthat will lter out the rays of light that would cause the strip tochange its color sensitivity to the gas.

Since the color of the filter makes the strip seen through it appearcolored, it is desirable to be able to compare the color of the portionof the strip viewed through pocket opening 9 with an adjoining portionof the strip that has not been exposed to the gas being detected. Thiscan be done by comparing the portion of the strip'viewed through thepocket opening with the adjoining portion seen through the window 10.The portion of the strip behind Window is not exposed to the atmospherebecause it is held tightly against the window by springs 13 behind it.

In the use of this dosimeter, it is attached to a persons clothing bymeans of clip 2, with the open side of the receptacle facing forward.Periodically, the wearer can lift up the dosimeter and look at thecolorimetric strip through the iilter window of the shield. If henotices that the color of the strip seen through shield window 24 andpocket opening 9 is different from the color of the strip behind thepocket window, he knows that the strip has been affected by the gas thatis being detected. He then presses down on tab 21 to swing the shieldout so that he can compare the real color of the strip with the colorstandards located around the pocket opening. If he does not already knowwhat exposure to gas is indicated by each color standard, he can getthat information from a chart that he carries, which also will tell himwhether or not the exposure is dangerous.

According to the provisions of the patent statutes, We have explainedthe principle of our invention and have illustrated and described whatWe now consider to represent its best embodiment. However, we desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specically illustrated anddescribed.

We claim:

1. A dosimeter comprising a receptacle having back and side walls and anopen front, means `for holding in the receptacle a colorimetric stripsensitive to light and a predetermined gas, a colorimetric stripsensitive to light and to a predetermined gas in said receptacle, ashield in the receptacle for normally covering the strip to protect itfrom direct light before and during exposure to said gas, the shieldbeing spaced from the back wall of the receptacle and from at least someof its side walls t0 expose lthe area behind the shield to thesurrounding atmosphere, means in said area for spacing the strip fromthe shield, color standards in the receptacle adjacent said holdingmeans, and means for temporarily moving the shield out of the receptaclefar enough to permit the color of said said standards'.

2. A dosimeter according to claim 1, including a hinge attaching saidshield to theV receptacle, and said shield moving means being a rigidtab projecting from the shield a short distance from the hinge.

3. A dosimeter according to claim 1, in which said strip-holding meansinclude a pocket formed in said back wall of the receptacle and providedwith a front opening, one end of the pocket outside of the receptaclehaving a slot `for insertion of a colorimetric strip behind said open-4. A dosimeter according to claim 3, including a clear transparentWindow forming part of the front of said pocket and located next to saidfront opening for engagement by the strip'.

5. A dosimeter according to claim 4, including spring means in saidpocket for pressing a colorimetric strip forward against said window.

6. A dosimeter according to claim 1, in which said shield is providedwith an opening therethrough, and a light lter is mounted in saidopening to form a window for viewing a colorimetric strip behind it.

7. A dosimeter according to claim 2, in which said shield is providedwith an opening therethrough, a light filter is mounted in said openingto 'form a Window for viewing a colorimetric strip behind it, a cleartransparent window is disposed behind the shield for covering part ofthe colorimetric strip, and spring means connected to the receptacle areadapted to press the strip forward against the transparent window.

References Cited UNITED STATES PATENTS 2,680,816 6/1954 Stern. 3,194,9637/1965 McKee. 3,283,153` 11/1966 Geiger.

MORRIS 0. WOLK, Primary Examiner R. M. REESE, Assistant Examiner U.S.Cl. XR. 23-253

